Polly is pushing a box to the right across the floor with a force of 30 N. The force of gravity is 8 N, and the normal force is 8 N. Which value could describe the force of friction if Polly could not move the box?
$\leftarrow 30 N$
$\leftarrow 8 N$
$\rightarrow 8 N$
$\rightarrow 30 N$
Answer (1)
Polly pushes a box with 30 N to the right.
The box does not move, indicating balanced forces.
Gravity (8 N down) and normal force (8 N up) cancel each other.
Friction must equal Polly's force to prevent movement, so the friction force is ← 30 N .
Explanation
Understanding the Problem The problem describes a scenario where Polly is pushing a box with a certain force, but the box doesn't move. We need to determine the force of friction acting on the box. Since the box is not moving, it means all the forces acting on it are balanced, resulting in a net force of zero.
Identifying the Forces The forces acting on the box are:
Polly's pushing force: 30 N to the right.
Force of gravity: 8 N downwards.
Normal force: 8 N upwards.
Force of friction: opposing the pushing force.
Balancing the Forces Since the box is not moving vertically, the force of gravity and the normal force are balanced. Therefore, we only need to consider the horizontal forces. For the box to remain stationary, the force of friction must be equal in magnitude and opposite in direction to Polly's pushing force.
Determining the Friction Force Therefore, the force of friction must be 30 N to the left to counteract Polly's 30 N force to the right.
Final Answer The force of friction is 30 N to the left.
Examples
Imagine you're trying to push a heavy couch across the floor, but it just won't budge. This problem illustrates the concept of static friction, which is the force that prevents the couch from moving. Understanding static friction is crucial in many real-world scenarios, such as designing brakes for cars or ensuring that objects stay in place on an inclined surface. By analyzing the forces acting on an object, we can determine the amount of force needed to overcome static friction and initiate movement, or conversely, the amount of friction required to maintain stability.
